On a plain English reading, manic depression was a poor name because it sounds like the mania is an attribute of the depression. Indeed, when I was kid, I was told that a family acquaintance suffered from this, and I figured it meant somebody who got depressed but in a slightly crazy way.
As as Permensoe says, a plain reading of polar is “of or at an extreme”. I tend to think that was precisely the intended meaning - isn’t a prominent diagnostic feature of bipolar disorder the tendency to occupy and sometimes swing between extremes, the lack of moderation in mood? I mean “occupying some point anywhere on the spectrum between extreme elation and dire unhappiness” is pretty much the definition of normal life!
I didn’t read this, it was explained to me, albeit by a clinician, who should know, but could have been wrong.
Anyway, when it was call “Manic Depression,” a lot of people weren’t presented for diagnosis, or families couldn’t understand the diagnosis, because the person was OK some of the time. People thought they had to be either manic or depressed 100% of the time. “Bipolar” was chosen because both “manic” and “depressive” were loaded terms-- and I think “mania” is even called something else now, but nevermind-- people wanted a term that didn’t sound like anything that had previous associations.
Most people don’t understand polarity the way a physicist does-- they understand it in terms of geography, or a magnet-- two ends of something, with some space in between, so they can conceptualize a person with “bipolar disorder” (“disorder” is an important part of the name-- the “bipolar” part is an adjective) as someone who spends too much time at one extreme or the other, but nonetheless, does at least sometimes spend some time somewhere in the middle.
Maybe something like “Mood spectrum disorder” would have been a more accurate descriptor, and I have no idea what terms were considered and rejected, but I think part of the point in choosing “bipolar disorder” was that is was sterile-- it didn’t sound like anything else already in use.
Another concern-- and this is just me talking now-- may have been that at one point some psychiatrists theorized that manic depression was a subtype of schizophrenia-- back when disorders were divided into “neurotic” and “psychotic” depending on whether there was a break with reality, there was a lot of debate over which type manic depression was, and so I think a new and completely unrelated term gave the disorder a fresh start away from its connection with schizophrenia, which no one now believes it to be a type of-- schizophrenics can have mood swings, but it’s not the same thing.
It’s been “Star” in the British Military since at least the last quarter of the 19th Century; the * denoting a modification from the previous mark of equipment (For example, the Short Magazine Lee-Enfield Mk III* differed from the Mk III in that it didn’t have a magazine cut-off or windage adjustable sights).
is still a pound sign, still a number sign, still a hash depending on context. A hashtag, on the other hand, is a hash followed by one or more characters, as in #hashtag. If you put a hash by itself in a tweet it will not be turned into a link.
^^Well, that’s the way it started out, but, yeah, # also is called a hashtag by itself, now, too. Call it a metonymy or synecdoche. I think either one might apply.
